7. PROJECT SUMMARY Riding with an Impaired (RWI) driver and Driving While Impaired (DWI) is prevalent among high school students. Motor vehicle crashes have remained the leading cause of death among adolescents for decades. In 2015, the U.S. encountered the largest percent increase in motor vehicle crash fatalities in 50 years. This included a significant increase in alcohol-impaired driving fatalities with 1 alcohol-impaired driving death occurring every 51 minutes and 1 in every 5 deaths occurring in passengers. Still, alcohol and marijuana continue as the drugs of choice for American youth and despite a slow secular decline in use during high school, annual prevalence remains high. Several factors predict future RWI/DWI in high school students, such as heavy episodic drinking, perceived peer norms of alcohol/substance use, low parental monitoring knowledge, and exposure to RWI. Recent studies also demonstrate the intimate relationship between RWI/DWI and household-adult exposure and behavior modeling. Extensive adolescent alcohol/drug use trajectory-related research has explored emerging adulthood outcomes (e.g. health, employment, college enrollment). However, despite the well-known relationship between transportation access and these domains, little is known about these outcomes as a direct result of exposure and engagement in RWI/DWI. Further, current studies largely do not explain how RWI/DWI exposure and participation develops. Given the complexity of the processes that may affect RWI/DWI, a social ecological theoretical framework is needed for systematic and full characterization of the relationships (multi-level influences), and interactions (social environmental) that shape emerging adulthood outcomes. We propose a highly novel multistage mixed methods study that employs the Ecodevelopmental Theoretical (ET) framework to characterize adolescent RWI/DWI behaviors and determine their association with health, employment, and higher education enrollment in emerging adulthood. First, we will analyze 7 waves of longitudinal adolescent health data (NIH's NEXT Generation Health Study - following U.S. 10th graders since Spring semester of the 2009-2010 academic year until the current date) in order to characterize RWI/DWI trajectory classes and their relationship to health, employment, and higher education enrollment in emerging adulthood. Next, we will use mixed methods to generate ET- driven hypotheses about how RWI/DWI exposure and participation develops and affects emerging adulthood outcomes within the context of peer, family, school, and environmental influences. Finally, we will use system dynamics modeling to build an explanatory model for observed outcome differences according to RWI/DWI trajectory classes. Our final theory driven explanatory model will advance the understanding of adolescent RWI/DWI behaviors and inform the subsequent development of an innovative and multi-level intervention focused on prevention of RWI/DWI and the enhancement of successful transitions of adolescents into emerging adulthood.